Vegetation has long been believed to be essential for forming river meanders, leading to the assumption that meandering channels could only form in vegetated landscapes. This belief was supported by evidence from the fossil record, which showed that meandering rivers were scarce before the rise of vascular land plants on Earth about 440 million years ago. Flume experiments also demonstrated that vegetation helps in transitioning from multi-thread to single-thread rivers, resulting in relatively narrow and deep channels with low width-to-depth ratios.

However, increasing empirical evidence and physics-based modeling suggest that meandering rivers can also form in landscapes without vegetation. As long as other cohesive agents, such as mud, provide the bank strength required to sustain meandering river planforms, meandering rivers can develop in these landscapes.

A recent study published in Nature Communications analyzed the planform morphology and migration dynamics of 54 modern meandering rivers. The study found that denser riparian vegetation correlates with a more sinuous and asymmetric shape of meander bends. However, the correlation is subtle, and it is difficult to infer a direct control of vegetation on meander shape due to the presence of other relevant confounding factors.

An international team of researchers, led by Alvise Finotello from the Department of Geosciences at the University of Padua, conducted the study.

“Unvegetated meandering rivers have now been recognized on several continents on Earth and also in extraterrestrial body, such as Mars, where vegetation most likely never existed. Our results demonstrate how the presence of vegetation correlates with the presence of meanders that are more sinuous and more asymmetric from a platform standpoint. However, inferring a direct control of vegetation on the morphology of meanders is difficult because other confounding factors make the correlation spurious”, Dr. Finotello explains.

“Still, we were able to show that vegetation actively reduces the rate at which rivers move laterally, and make lateral migration rates much more dependent on the curvature of river channel”, Dr. Finotello adds.

These findings provide new insights into the morphodynamics of meandering rivers on Earth. They are also important for reconstructing their evolution on extraterrestrial landscapes where records of ancient vegetation are absent.

Link to research: https://www.nature.com/articles/s41467-024-46292-x

Title: Vegetation enhances curvature-driven dynamics in meandering rivers

Authors: Alvise Finotello, Alessandro Ielpi, Mathieu G. A. Lapôtre, Eli D. Lazarus, Massimiliano Ghinassi, Luca Carniello, Serena Favaro, Davide Tognin & Andrea D’Alpaos